A printer or copier according to the electrophotographic principle with which color printing can be conducted is described in WO 98/39691; the content of WO 98/39691 is herewith incorporated into the disclosure of this specification. In FIG. 1, a principle image of a printer DR according to WO 98/39691 is presented that is drawn upon to explain the preferred embodiment. Character generators ZG (for example on both sides of a final image carrier AT, for example a paper web) generate on a charge image carrier OPC (for example a photoconductor belt) charge images of the images to be printed. These are inked with toner into toner images in a developer station ES. The toner images are subsequently transferred in succession to an intermediate carrier TFB (for example a transfer belt)—in the following this transfer location is called a transfer printing station U1—and are collected there into a complete toner image. This is transfer-printed onto the final image carrier AT (in the following this transfer location is called a transfer printing station U2) and is subsequently fixed there. The printing according to WO 98/39691 and FIG. 1 can occur on both sides of the final image carrier AT. Refer to WO 98/39691 for details.
Upon generation of a multicolor image, the printer DR transitions into a start/stop operation. While the final image carrier AT stands still, the colors are collected on the intermediate carrier TFB (the transfer belt) into a complete color toner image (one collection cycle length thereby corresponds to the number of the color*transfer belt length). The final image carrier AT is then started so that the complete color toner image on the intermediate carrier TFB is transfer-printed precisely, line-by-line, onto the preceding print image on the final image carrier AT at the transfer printing station U2.
The chronological path of the creation of a print image, from the generation of the charge image on the oscillating circuit (in the following a photoconductor belt OPC) up to the transfer-printing onto the final image carrier AT is shown using FIG. 2; it is thereby assumed that the print image is composed of two colors F1 and F2. The charge image is respectively generated by a character generator ZG from the two colors F1 and F2 in succession on the photoconductor belt OPC (line Z1). The position of the toned charge image of the two colors F1 and F2 at the transfer printing station U1 is shown in line Z2 relative to the intermediate carrier (in the following a transfer belt TFB). Line Z3 shows the generation of the complete color toner image on the transfer belt TFB at the transfer printing station U2, and the position of the complete color toner image B transfer-printed onto the final image carrier AT results from line Z4. It is to be recognized that the complete color toner image B is generated on the transfer belt TFB (line Z3) from the successive colors Fl and F2 transferred onto the transfer belt TFB, and then the complete color toner image B is transfer-printed onto the final image carrier AT. The complete color toner image is then fixed on the final image carrier AT in a known manner (can be learned from WO 98/39691). For transfer-printing of the complete color toner image B from the transfer belt TFB onto the final image carrier AT, this is started, accelerated to printing speed and then pivoted onto the transfer belt TFB (region A1 in line Z4); after the transfer printing the final image carrier AT is pivoted away from the transfer belt TFB (region A2 in line Z4) and stopped again. Due to the pivoting motion (regions A1 and A2) of the final image carrier AT onto or away from the transfer belt TFB, vibrations are generated therein that can affect the photoconductor belt OPC via the transfer belt TFB and can lead to the situation that the toner images of the two colors Fl and F2 shift somewhat, with the result that the colors Fl and F2 no longer exactly overlap on the transfer belt TFB. This situation is represented in FIG. 2 by the dashed lines L1 and L2 running vertically. It is to be recognized that the dashed lines L1, L2, and therefore the vibrations, affect the photoconductor belt OPC, and in fact the character generator ZG and the transfer printing station U1.
A method with which both color images and monochrome images can be generated with an electrophotographic printer is known from EP 1 562 084 A2. For this, charge images of the images are generated on a charge image carrier, these are inked with toner, the toner images are transfer-printed onto a transfer belt in a first transfer printing process and from there onto a recording medium (for example a paper sheet). For this purpose, the recording medium is pivoted onto the transfer belt. Via the pivoting of the recording medium onto the transfer belt, vibrations are generated therein and the charge image carrier that lead to unwanted displacements of the toner images on the transfer belt. This is in particular disadvantageous in color printing since then the individual color toner images of a color image that are collected on the transfer belt no longer come to lie exactly atop one another. In order to avoid this disadvantage given color images generated from four color toners, it is proposed to use color toner of a yellow color as a last color in the color collection cycle since the human eye registers the shift of the yellow color toner image least in comparison to the other color toner images.
DE 103 45 149 A1 deals with a problem that arises in that a second belt is pivoted onto or away from a revolving first belt. A slack at the drive roller for the first belt is generated by the load, with the consequence that the revolution speed of the first belt changes. This is disadvantageous when the belt is a transfer belt in an electrographic printer. Solutions of how the slack can be avoided are now proposed.